Getting more ZZZ's at night doesn't necessarily translate to more A's on report cards, according to a new study that examines college students' sleeping habits.

The study -- presented last month at "SLEEP 2011," a meeting of the Associated Professional Sleep Societies -- found that although a class schedule with later start times allows college students to get more sleep, it also gives them more time to stay out drinking at night. As a result, their grades tend to suffer.

"Later class start times seemed to change the choices students make: They sleep longer, and they drink more," said co-lead author Pamela Thacher, associate professor of the Department of Psychology at St. Lawrence University in Canton, N.Y.

Thacher speculated that drinking more alcohol, which is known to disrupt sleep, may reduce the benefits of getting more sleep.

"The effects of later class start times might include more sleep," she said in a news release. "But this might be offset by lower quality sleep, which in turn might affect their ability to engage, intellectually, with their coursework."

At the University of Colorado, students say they try to craft their schedules around the times they feel most awake.

Nyall Hasty, a CU junior, was taking a late afternoon biology course.

"I just woke up from a nap," he said, as he emerged from his class at about 4 p.m. He said he dozed off during a lecture on photosynthesis.

Ideally, he'd take classes from 10 a.m. to 1 p.m., he said, because he gets sleepy in the afternoon. He agrees with the study that when students have later classes it tempts them to stay out later.

CU junior Ariel Aguilar, who is studying computer science and psychology, said she tends to stack her classes up in the morning. During her freshman year, Aguilar said, she made the mistake of taking to many continuous classes that ran late into the afternoon and would fall asleep in her programming course.

Thacher, co-author Serge Onyper and their research team studied 253 college students.

The authors noted that the results are much different from previous studies of school start times in middle and high school. Those studies show numerous benefits of later school start times, which tend to decrease truancy, improve mood and indirectly promote learning.

In a study published in 2008 in Behavioral Sleep Medicine, Thacher found that 60 percent of student participants at a liberal-arts college reported engaging in a single night of total sleep deprivation once or more since starting college. Statistical analyses found that pulling an "all-nighter" was associated with lower grades.